Abstract Background Many studies have evaluated the role of individual nutrients on the development of psoriasis. However, only few studies have investigated the effect of a healthy eating pattern, such as the Mediterranean diet. In this study, we aimed to investigate the relationship between adherence to the Mediterranean diet, the body composition and the severity of psoriasis in a group of naïve-treatment patients with psoriasis. Methods This is a cross-sectional case–control observational study. Sixty-two patients (49 males and 13 females, mean age: 50.2±10.5yrs) affected with mild-to-severe psoriasis were consecutively enrolled. Sixty-two age-, sex- and body mass index (BMI)-matched healthy subjects served as control group. A validated 14-item questionnaire (PREDIMED: PREvención con DIeta MEDiterránea) was used for the assessment of adherence to the Mediterranean diet. The severity of psoriasis was by assessed by standardized Psoriasis Area and Severity Index (PASI) score and C-reactive protein (CRP) levels. Body composition was analyzed with bioelectrical impedance analysis. Results A higher percentage of psoriatic patients had a lower PREDIMED score compared to the control group (30.6% vs 4.8%). PASI score was significantly associated with the percentage of fat mass (FM%) and CRP levels. PASI score and CRP levels were significantly associated with the dietary components included in the PREDIMED questionnaire or with the PREDIMED score. At multiple regression analysis, the major predictor of PASI score were FM among BIA parameters, (r 2 =0.537, β=0.740, p